Process for producing enlarged latex

ABSTRACT

A process for preparing an enlarged latex, which comprises (1) causing (a) an anionic surfactant and (b) at least one surfactant selected from the group consisting of a cationic surfactant and an amphoteric surfactant to exist in a latex, (2) adding, as an aggregating and enlarging agent, at least one selected from the group consisting of (i) an inorganic acid, (ii) an organic acid, (iii) a substance which forms an acid in water, (iv) a combination of at least two substances which are reacted with each other to form an acid, and (v) a substance which forms an acid by exposure to active rays to the latex in the presence of these surfactants, and (3) causing the acid derived from the aggregating and enlarging agent to act on the latex, thereby enlarging the particle diameter of the latex, an enlarged latex obtained by the preparation process, a graft copolymer obtained by polymerizing a polymerizable monomer with the enlarged latex, and a resin composition comprising the graft copolymer and a thermoplastic resin.

TECHNICAL FIELD

[0001] The present invention relates to a process for preparing anenlarged latex having a larger particle diameter by enlarging a latex byaggregation, and more particularly to a process for preparing anenlarged latex, which is economical and high in productivity and permitsenlarging a latex while retaining the stability of the latex. Thepresent invention relates to a process for preparing a graft copolymermaking use of such an enlarged latex, a resin composition containing thegraft copolymer and a thermoplastic resin, etc.

BACKGROUND ART

[0002] A latex is an emulsion in which a polymer such as rubber or aplastic is dispersed in the form of colloid in water by an emulsifyingagent. As synthetic latices, are prepared, for example, rubber laticessuch as styrene-butadiene rubber latices, acrylonitrile-butadiene rubberlatices and polychloroprene rubber latices; and resin latices such asvinyl acetate (co)polymer latices, styrene (co)polymer latices andacrylic ester (co)polymer latices by emulsion polymerization. Thelatices are used in a wide variety of fields such as a field ofsynthetic resins, a field of paints, a field of treating agents of paperand fabrics and a field of civil engineering such as concrete andasphalt.

[0003] A latex is generally an emulsion in which a polymer having a fineparticle diameter is dispersed. However, a latex having a largerparticle diameter is required in many application fields as necessaryfor the end application intended. A graft copolymer obtained bypolymerizing a vinyl monomer in the presence of a rubber latex is usedas an impact modifier or the like for thermoplastic resins. In suchgraft copolymers, those having various particle diameters are chosen foruse as necessary for the end application intended. In order to obtain agraft copolymer having a large particle diameter, a latex having a largeparticle diameter is preferably used.

[0004] A latex is generally prepared by an emulsion polymerizationprocess. However, it takes a long polymerization time to obtain a latexhaving a large particle diameter by a seed polymerization process, sothat productivity is lowered. In particular, when a diene monomer or amonomer mixture containing a diene monomer and a vinyl monomer will bepolymerized by the seed polymerization process to obtain a latex havinga large particle diameter, it takes a very long polymerization time. Asa process for obtaining a latex having a large particle diameter in ashort period of time, there has heretofore been proposed a process inwhich an inorganic acid, an organic acid, a salt, a polymeric flocculantand/or a latex for enlargement is added to a latex having a smallparticle diameter to enlarge the latex by aggregation.

[0005] For example, Japanese Patent Application Laid-Open No. 71603/1997has proposed a process in which so mild shear as to produce no rubberlump is applied to a diene polymer rubber latex obtained by emulsionpolymerization to enlarge the latex by aggregation mainly by virtue ofBrownian aggregation while facilitating mixing of a flocculant. TheBrownian aggregation means that latex particles undergo Brownianmovement, thereby colliding with one another to aggregate. Morespecifically, the process comprises lowering the number of revolutionsupon stirring in enlargement of the latex by aggregation making use ofthe flocculent to conduct aggregation mainly by virtue of Brownianmovement, thereby inhibiting the formation of aggregated lumps toenlarge the latex by aggregation. This process uses shear aggregation bya stirring blade and Brownian aggregation in combination. According tothis process, particles of the latex can be enlarged to a certainextent. However, the particles cannot be enlarged to a sufficient extentjudging from Examples thereof. In addition, in this process, an acid isused as a flocculant, and the flocculant is added so as to keep the pHof the system at 5 or lower. When it is intended to raise the pH of thesystem by adding a basic substance to the enlarged latex obtained bythis process so as to stabilize the latex, however, the stability of thelatex becomes insufficient due to a high salt concentration in thesystem. Therefore, when graft polymerization of a vinyl monomer has beenattempted in the presence of said latex, a problem that deposit is easyto be formed has arisen.

[0006] Japanese Patent Publication No. 2229/1969 has proposed a processin which a formaldehydesulfoxylate and a peroxide are added to anaqueous dispersion containing fine particles of a butadiene polymer toenlarge the particles while causing graft polymerization to progress byadding a monomer to the dispersion. According to this process, however,it is difficult to enlarge the particles to a sufficient extent.

[0007] Japanese Patent Application Laid-Open No. 45921/1981 has proposeda process in which an acrylic ester-unsaturated acid copolymer latexobtained by polymerization in the presence of an anionic surfactant andhaving a pH of 4 or higher is added to a synthetic rubber latex the pHof which has been adjusted to 7 or higher, thereby enlarging theparticle diameter of the synthetic rubber latex. According to thisprocess, however, it is necessary to separately prepare the latex forenlargement. Therefore, this process is complicated in operation and notpreferable from the economical point of view. In addition, when graftpolymerization of a vinyl monomer has been attempted in the presence ofthe synthetic rubber latex enlarged by adding such an acrylicester-unsaturated acid copolymer latex, a problem that the stability ofthe latex is impaired to form aggregated lumps has arisen.

DISCLOSURE OF THE INVENTION

[0008] It is an object of the present invention to provide a process forpreparing an enlarged latex, which is economical and high inproductivity and permits enlarging a latex while retaining the stabilityof the latex.

[0009] Another object of the present invention is to provide a processfor preparing an enlarged latex the stability of which is not impairedeven when a polymerizable monomer is graft polymerized in the presenceof the enlarged latex.

[0010] A further object of the present invention is to provide anenlarged latex having such excellent various properties, a process forpreparing a graft copolymer by polymerizing a polymerizable monomer inthe presence of such an enlarged latex, a resin composition containingthe graft copolymer and a thermoplastic resin, and a graft copolymer(latex, slurry or particles) having an even particle diameterdistribution.

[0011] The present inventors have carried out an extensive investigationwith a view toward achieving the above objects. As a result, it has beenconceived to cause an anionic surfactant and a cationic surfactantand/or an amphoteric surfactant to exist in a latex and add an acid or asubstance capable of forming an acid as an aggregating and enlargingagent thereto to cause the acid to act, thereby enlarging the particlediameter of the latex.

[0012] When the pH of a latex stabilized by an anionic surfactant islowered by an acid, the primary particles of the latex are aggregatedand enlarged. However, the stabilizing effect by the anionic surfactantbecomes weak as the pH is lowered, so that the stability of the latextends to be impaired. On the other hand, when an anionic surfactant anda cationic surfactant and/or an amphoteric surfactant are caused toexist in a latex, (1) the system is stable by virtue of the stabilizingeffect by the anionic surfactant when the pH is high, (2) thestabilizing effect by the anionic surfactant is weakened when the pH islowered by an acid, so that aggregation and enlargement of latexparticles occur, and (3) the system is stabilized again by virtue of thestabilizing effect by the cationic surfactant and/or the amphotericsurfactant when the pH is more lowered. As a result, a stabilizedenlarged latex can be obtained. Even when the stabilized enlarged latexis used in a graft polymerization reaction, the stability of the systemis not impaired.

[0013] When the lowering of the pH in this process is conducted by usinga combination of at least two substances which are reacted with eachother to form an acid, such as a combination of hydrogen peroxide with aformaldehydesulfoxylate, and enlargement by aggregation is conducted byBrownian aggregation without conducting stirring during the enlargementby aggregation, an enlarged latex having a narrow particle diameterdistribution and a large particle diameter can be stably formed.

[0014] A graft copolymer obtained by graft polymerizing a polymerizablemonomer on the enlarged latex obtained by the process according to thepresent invention can be used in various application fields by itselfand also exhibits excellent properties as an impact modifier forthermoplastic resins. The present invention has been led to completionon the basis of these findings.

[0015] According to the present invention, there is thus provided aprocess for preparing an enlarged latex by enlarging a latex byaggregation, which comprises (1) causing

[0016] (a) an anionic surfactant and

[0017] (b) at least one surfactant selected from the group consisting ofa cationic surfactant and an amphoteric surfactant to exist in thelatex, (2) adding, as an aggregating and enlarging agent, at least oneselected from the group consisting of:

[0018] (i) an inorganic acid,

[0019] (ii) an organic acid,

[0020] (iii) a substance which forms an acid in water,

[0021] (iv) a combination of at least two substances which are reactedwith each other to form an acid, and

[0022] (v) a substance which forms an acid by exposure to active rays tothe latex in the presence of these surfactants, and (3) causing the acidderived from the aggregating and enlarging agent to act on the latex,thereby enlarging the particle diameter of the latex.

[0023] According to the present invention, there is also provided anenlarged latex obtained by the preparation process described above.According to the present invention, there are further provided a processfor preparing a graft copolymer, which comprises polymerizing apolymerizable monomer in the presence of the enlarged latex describedabove, and a resin composition comprising the graft copolymer obtainedby this preparation process and a thermoplastic resin.

[0024] According to the present invention, there is still furtherprovided a graft copolymer containing an anionic surfactant and at leastone surfactant selected from the group consisting of a cationicsurfactant and an amphoteric surfactant and having a ratio (Dv/Dn) ofthe volume average particle diameter (Dv) to the number average particlediameter (Dn) of 1.2 to 1.8.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] 1. Latex:

[0026] A latex used in the present invention may be that prepared by anyprocess. However, a latex synthesized by emulsion polymerization isgenerally used. No particular limitation is imposed on componentsforming the latex. As examples thereof, however, may be mentioned(co)polymers of diene monomers such as butadiene, isoprene andchloroprene; (co)polymers of vinyl monomers such as styrene,acrylonitrile, acrylic esters, methacrylic esters, ethylene, vinylchloride, vinylidene chloride, vinyl acetate and vinyl fluoride;copolymers of a diene monomer with a vinyl monomer; silicone resins suchas polyorganosiloxanes; and polyester, epoxy resins, melamine resins,polyamide and polyurethane. These polymers may be used either singly orin any combination thereof. The latex may have a structure such as acore/shell structure and be an organic.inorganic composite latex.

[0027] In order to regulate a surface charge of the latex to control theenlargement by aggregation, a latex obtained by copolymerizing such adiene monomer and/or vinyl monomer as described above with a monomerhaving an anionic and/or cationic functional group may also be used.Examples of the monomer having the functional group include acrylicacid, methacrylic acid, itaconic acid, fumaric acid, acrylamide,methacrylamide, hydroxyethyl methacrylate, hydroxyethyl acrylate andglycidyl methacrylate. Further, a crosslinkable monomer such asdivinylbenzene, ethylene glycol dimethacrylate, trimethylolpropanetrimethacrylate or 1,3-butanediol diacrylate may be used in combination.

[0028] Upon polymerization of the latex, a radical polymerizationinitiator, heat decomposable polymerization initiator, redox initiatoror the like may be used. Besides, light, X-rays or the like may also beused. A chain transfer agent such as t-dodecylmercaptan,n-octylmercaptan or α-methylstyrene dimer may be used upon thepolymerization as needed. Surfactants are used upon the polymerization.Regarding this, however, description will be given subsequently.

[0029] These latices may be used either singly or in any combinationthereof. Of these, the (co)polymer latices of diene monomers,(co)polymer latices of vinyl monomers, and copolymer latices of a dienemonomer with a vinyl monomer are preferred. When the process accordingto the present invention is applied to a diene (co)polymer latexcontaining a diene monomer such as butadiene, a great effect isachieved, and particularly preferable results are yields from theviewpoint of shortening of polymerization time.

[0030] Examples of the diene (co)polymer latex include (co)polymerlatices of diene monomers such as butadiene, isoprene and chloroprene;and copolymer latices of a diene monomer with a vinyl monomer. Examplesof the vinyl monomer copolymerized with the diene monomer includearomatic vinyl monomers such as styrene and α-methylstyrene; alkyl(meth)acrylate monomers such as methyl methacrylate and n-butylacrylate; and unsaturated nitrile monomers such as acrylonitrile.Example of the (co)polymer latices of the diene monomers includepolybutadiene latices. Examples of the diene copolymer include copolymerrubbers of a diene monomer such as butadiene with a vinyl monomer suchas styrene. No particular limitation is imposed on the copolymerizationratio of the diene monomer to the vinyl monomer. However, for example,copolymers of 50 to 99 wt. % of a diene monomer with 1 to 50 wt. % of avinyl monomer may be mentioned.

[0031] No particular limitation is imposed on the particle diameter(volume average particle diameter) of the latex. However, it ispreferably 200 nm or smaller, more preferably 150 nm or smaller becauseeven a latex having a fine particle diameter of 150 nm or smaller,furthermore 100 nm or smaller can be effectively enlarged by the processaccording to the present invention.

[0032] 2. Surfactant:

[0033] In the present invention, (a) an anionic surfactant and (b) atleast one surfactant selected from the group consisting of a cationicsurfactant and an amphoteric surfactant are caused to exist in thelatex. As an example of a process for causing these surfactants to existin the latex, is mentioned a process in which emulsion polymerization isconducted with the anionic surfactant upon preparation of the latex, andthe cationic surfactant and/or the amphoteric surfactant is then addedto the resultant latex. When the cationic surfactant and/or theamphoteric surfactant is added to the latex containing the anionicsurfactant, however, deposit may be formed in some cases. In such acase, is preferred a process in which the cationic surfactant and/or theamphoteric surfactant has been added in advance together with theanionic surfactant upon the preparation of the latex. In order toprevent the formation of the deposit, a process in which polymerizationis conducted with the anionic surfactant, and the cationic surfactantand/or the amphoteric surfactant is added during or after thepolymerization in a state that the cationic surfactant and/or theamphoteric surfactant has been mixed with an excess amount of theanionic surfactant may also be adopted.

[0034] As examples of the anionic surfactant, may be mentioned thosecommonly used in emulsion polymerization, such as carboxylic acid salts,sulfonic acid salts, sulfuric ester salts and phosphoric ester salts. Ofthese, are preferred the carboxylate type surfactants, for example,alkali metal salts of higher fatty acids, such as sodium oleate,potassium oleate, sodium stearate, potassium stearate, sodium myristate,potassium myristate, sodium palmitate, potassium palmitate, potassiumlaurate, potassium undecanate, sodium linolate, potassium linolate,potassium caprylate, potassium nonanate and potassium caprinate; alkalimetal salts of rosinic acid, such as disproportionating potassiumrosinate; alkali metal salts of alkylsarcosinic acids; and alkali metalsalts of alkenylsuccinic acids. These anionic surfactants may be usedeither singly or in any combination. When a carboxylate type anionicsurfactant is used, a sulfonate type anionic surfactant and a nonionicsurfactant may be used as assistant in combination.

[0035] Examples of the cationic surfactant include quaternary ammoniumsalts having at least one alkyl group, primary to tertiary amine saltshaving at least one alkyl group, alkylphosphonium salts andalkylsulfonium salts. More specifically, as examples thereof, may bementioned benzalkonium chloride, alkyltrimethylammonium chlorides,alkylamine acetates, alkylamine hydrochlorides, dialkyldimethylammoniumchloride, alkylisoquinolinium chlorides and alkylisoquinoliniumbromides.

[0036] As examples of the amphoteric surfactant, may be mentionedbetaines such as N-octylbetaine, N-decylbetaine, N-undecylbetaine,N-dodecylbetaine, N-tetradecylbetaine, N-hexadecylbetaine, octylbetaine,decylbetaine and dodecylbetaine; carboxylic acid type amphotericsurfactants containing a betaine such as sulfobetaine or sulfatebetaine;sulfate type amphoteric surfactants, such as hydroxyethylimidazolinesulfate; and sulfonic acid type amphoteric surfactants such asimidazolinesulfonic acid.

[0037] The surfactants selected from the group consisting of thecationic surfactants and amphoteric surfactants may be used eithersingly or in any combination thereof. No particular limitation isimposed on the using ratio of (a) the anionic surfactant to (b) thecationic surfactant and/or the amphoteric surfactant. It is howeverdesirable that (b) the cationic surfactant and/or the amphotericsurfactant be caused to exist in a proportion of preferably 0.01 to 100mol, more preferably 0.1 to 80 mol, still more preferably 1 to 50 molper 100 mol of (a) the anionic surfactant from the viewpoints ofstability of the latex, control of enlargement by aggregation andstability of the enlarged latex. The surfactants are generally used in aproportion of 0.1 to 5 parts by weight in total per 100 parts by weightof the (co)polymer component in the latex or the monomer(s) forming the(co)polymer component.

[0038] 3. Aggregating and Enlarging Agent:

[0039] In the present invention, at least one selected from the groupconsisting of (i) an inorganic acid, (ii) an organic acid, (iii) asubstance which forms an acid in water, (iv) a combination of at leasttwo substances which are reacted with each other to form an acid, and(v) a substance which forms an acid by exposure to active rays is usedas an aggregating and enlarging agent.

[0040] As examples of the inorganic acid, may be mentioned hydrochloricacid, sulfuric acid, nitric acid and phosphoric acid. As examples of theorganic acid, may be mentioned acetic acid, formic acid, tartaric acid,malic acid and butyric acid. As examples of the substance which forms anacid in water, may be mentioned acid anhydrides such as acetic anhydrideand maleic anhydride; and esters such as sulfuric esters and phosphoricesters.

[0041] As the combination of at least two substances which are reactedwith each other to form an acid, is preferred a combination ofsubstances which form an acid by a redox reaction, and specific examplesthereof may include combinations of peroxide/formaldehyde,peroxide/sulfoxylic acid salt and peroxide/formaldehydesulfoxylate. Ofthese, the combination of peroxide/formaldehydesulfoxylate (for example,sodium formaldehydesulfoxylate) is preferred.

[0042] No particular limitation is imposed on the substance which formsan acid by exposure to active rays so far as it is a substance whichforms a Brφnsted acid or Lewis acid by exposure to active rays. Specificexamples thereof include onium salts, halogenated organic compounds,quinonediazide compounds, α,α-bis(sulfonyl)diazomethane compounds,α-carbonyl-α-sulfonyl-diazomethane compounds, sulfonic compounds,organic ester compounds, organic acid amide compounds and organic acidimide compounds. Examples of the active rays include ultraviolet rays,far ultraviolet rays, electron rays and laser beams.

[0043] These acids and acid-forming substances are generally added inthe form of an aqueous solution to the latex. With respect to the amountadded, it is desired that an amount in which the enlargement of thelatex is easy to be achieved within limits not forming any aggregatedlump of the latex be confirmed by experiments, since the acidity variesaccording to the kind of the acid or acid-forming substance. Preferableexperimental examples in this respect are specifically shown inrespective Examples.

[0044] In order to adjust the particle diameter of the enlarged latex,the aggregating and enlarging agent and a salt may be used incombination. The salt may be contained in the latex in advance or addedprior to an enlarging treatment by aggregation. Examples of salts havingno pH-buffering effect include sodium chloride, potassium chloride andcalcium chloride. Examples of salts having a pH-buffering effect includesodium pyrophosphate, sodium carbonate and ammonium sulfate.

[0045] 4. Enlarging treatment:

[0046] In the present invention, the acid derived from the aggregatingand enlarging agent is caused to act on a latex, thereby enlarging theparticle diameter of the latex. More specifically, an anionic surfactantand a cationic surfactant and/or an amphoteric surfactant are caused toexist in the latex, and an acid or acid-forming substance is added asthe aggregating and enlarging agent to the latex, thereby causing theacid derived from the aggregating and enlarging agent to act on thelatex. When the aggregating and enlarging agent is an inorganic acid, anorganic acid or a substance which forms an acid in water, the acidimmediately performs an aggregating and enlarging action in the latex.

[0047] When the aggregating and enlarging agent is a combination of atleast two substances which are reacted with each other to form an acid,a chemical reaction between these substance takes place in the latex toform an acid, and said acid performs an aggregating and enlargingaction. When the aggregating and enlarging agent is a substance whichforms an acid by exposure to active rays, the latex is exposed to theactive rays to form an acid, and the acid thus formed performs anaggregating and enlarging action.

[0048] In order to enhance the enlarging effect upon the enlargingtreatment by aggregation, ultrasonic vibration may be applied. Noparticular limitation is imposed on the treating temperature upon theenlargement by aggregation. However, it is preferably 20 to 90° C. thatis a temperature generally easy to control, more preferably atemperature not lower than the glass transition temperature of thepolymer component forming the latex.

[0049] The enlarging treatment by aggregation may be conducted whilestirring the latex. However, the stirring may be stopped after theaggregating and enlarging agent is added, and stirring and mixing arelightly conducted so as to uniformly disperse. When no stirring of thelatex is conducted, the enlargement of the latex takes place by Brownianaggregation of latex particles. When the aggregating and enlarging agentis the combination of at least two substances which are reacted witheach other to form an acid, or the substance which forms an acid byexposure to active rays in particular, a method in which the latex isenlarged by Brownian aggregation without conducting stirring of thelatex in the step of causing the acid to act on the latex is preferredfrom the viewpoint of providing an enlarged latex narrow in particlediameter distribution represented by a ratio (Dv/Dn) of the volumeaverage particle diameter (Dv) to the number average particle diameter(Dn). In this case, it is considered that the formation of the acid inthe system and Brownian aggregation by the action of the acid are causedto progress in well balanced relation, and consequently a latex having anarrow particle diameter distribution and uniformly enlarged is formed.The latex having a narrow particle diameter distribution and uniformlyenlarged can exhibit high quality and high performance when it is usedin various fields.

[0050] After the enlarging treatment of the latex, a basic substancesuch as sodium hydroxide, potassium hydroxide, sodium carbonate orpotassium carbonate is generally added to the latex to neutralize theacid. These basis substances are generally added in the form of anaqueous solution to the latex.

[0051] No particular limitation is imposed on the particle diameter ofthe enlarged latex. However, it is generally 150 nm or greater,preferably about 200 to 1,000 nm in terms of the volume average particlediameter (Dv) thereof. Even when the process according to the presentinvention is applied to a latex having a fine particle diameter, thelatex can be enlarged to a volume average particle diameter ofpreferably 200 nm or greater, more preferably 250 nm or greater. Thelatex may be enlarged to 300 nm or greater, furthermore 350 nm orgreater as needed. When the volume average particle diameter is enlargedto 300 nm or greater in particular, the effect of the present inventionis markedly exhibited. No particular limitation is imposed on theparticle diameter distribution (Dv/Dn) of the enlarged latex. Accordingto the process of the present invention, however, an enlarged latexhaving an even particle diameter of preferably 1.2 to 1.8, morepreferably 1.2 to 1.6, still more preferably 1.2 to 1.5 in terms ofDv/Dn can be provided.

[0052] 5. Graft Polymerization and Graft Copolymer:

[0053] The enlarged latex obtained by the process described above issubjected to graft polymerization, whereby a graft copolymer can beobtained. The graft polymerization can be conducted by polymerizing apolymerizable monomer in the presence of the enlarged latex. Noparticular limitation is imposed to a graft polymerization process.However, an emulsion polymerization process and a suspensionpolymerization process are preferred. Upon the graft polymerization, asurfactant such as an anionic surfactant, cationic surfactant,amphoteric surfactant or nonionic surfactant; a suspending agent such asan organic suspending agent or inorganic suspending agent; etc. may besuitably added to more stabilize the system. No particular limitation isimposed on the polymerizable monomer used in the graft polymerization.However, it is preferably a vinyl monomer. No particular limitation isalso imposed on the weight ratio of the enlarged latex to thepolymerizable monomer. However, they are preferably graft polymerized insuch proportions that the solid content of the enlarged latex is 5 to 95wt. %, and the content of the vinyl monomer is 95 to 5 wt. %.

[0054] As examples of the vinyl monomer, may be mentioned aromatic vinylmonomers such as styrene and α-methylstyrene; aromatic polycyclic vinylmonomers such as 4-vinylbiphenyl and 2-vinylnaphthalene; unsaturatednitriles such as acrylonitrile and methacrylonitrile; alkyl(meth)acrylate monomers such as methyl methacrylate,and butyl acrylate;unsaturated carboxylic acids such as acrylic acid, methacrylic acid,maleic acid and maleic anhydride; and maleimide monomers such asmaleimide and N-phenylmaleimide. These vinyl monomers may be used eithersingly or in any combination thereof.

[0055] A polyfunctional vinyl monomer such as divinylbenzene, allylmethacrylate, ethylene glycol dimethacrylate or 1,3-butylenedimethacrylate may be suitable used in combination upon thepolymerization of the vinyl monomer. A chain transfer agent such ast-dodecylmercaptan or n-octylmercaptan may also be used.

[0056] The vinyl monomer graft polymerized on the enlarged latex may beadded into the reaction system at once, in several portions,continuously or in any combination thereof. When the graftpolymerization is conducted in two or more stages, the monomercompositions in respective stages may be the same or different from eachother.

[0057] When the graft polymerization is conducted with the enlargedlatex by emulsion polymerization or suspension polymerization, a graftcopolymer latex or slurry containing the anionic surfactant and thecationic surfactant and/or the amphoteric surfactant is provided. Theratio (Dv/Dn) of the volume average particle diameter (Dv) to the numberaverage particle diameter (Dn) in the graft copolymer according to thepresent invention is preferably 1.2 to 1.8, more preferably 1.2 to 1.6,still more preferably 1.2 to 1.5, and so the particle diameter thereofis even. In a graft copolymer obtained by conducting the graftpolymerization by suspension polymerization, however, the particlediameter distribution of a portion to be grafted does often notcorrespond to the particle diameter distribution of the graft copolymer.Therefore, the particle diameter distribution (Dv/Dn) of such a graftcopolymer is determined to mean the ratio of the volume average particlediameter to the number average particle diameter (Dn) in the portion tobe grafted.

[0058] Since the number of coarse particles becomes decreased by thenarrow particle diameter distribution of the graft copolymer anddeterioration of transparency caused by scattering of light due to thecoarse particle can be prevented, the transparency thereof can beenhanced. In addition, since particles having a particle diametereffective for enhancement of strength become increased by the narrowparticle diameter distribution of the graft copolymer, the strengththereof is also enhanced. It is preferred from the viewpoint oftransparency in particular that the kinds and combination of the vinylmonomers subjected to graft polymerization be selected in such a mannerthat the refractive indices of the polymer (enlarged latex particles) tobe grafted and the resulting graft copolymer consist with each other.For example, when the enlarged latex is a butadiene rubber latex orstyrene-butadiene rubber latex, styrene, methacrylic acid, butylacrylate, etc. are suitably combined as vinyl monomers subjected to thegraft polymerization, whereby the refractive indices of the polymer tobe grafted and the resulting graft copolymer can be caused to consistwith each other. It is preferred that a difference in refractive indexbetween the polymer to be grafted and the graft copolymer be 0.02 orsmaller.

[0059] The volume average particle diameter of the graft copolymer isgenerally 150 nm or greater, preferably about 200 to 1,000 nm. When thevolume average particle diameter is 300 nm or greater in particular, theeffect by the application of the present invention is marked. Asdescribed above, however, the volume average particle diameter of agraft copolymer obtained by conducting the graft polymerization by thesuspension polymerization is determined to mean the volume averageparticle diameter of the portion to be grafted.

[0060] After the graft polymerization, the graft copolymer is providedas a latex, slurry or particles separated and collected therefrom. Noparticular limitation is imposed on a method for separating andcollecting the graft copolymer as particles from the latex or slurry.However, as examples thereof, may be mentioned a method in which acoagulant such as hydrochloric acid or calcium chloride is added to thelatex to coagulate particles, and the resultant slurry is dehydrated anddried, and a method in which the latex is sprayed in heated air to dryit. In any method, additives such as antioxidants, ultravioletabsorbents, anti-blocking agents, pigments, fillers, lubricants,antistatic agents and antibacterial agents may be suitably added beforeor after the coagulation and drying. The graft copolymer may be used asa thermoplastic resin by itself. In such a case, dry particles may besubjected to molding or forming and processing as they are or afterpelletizing them. No particular limitation is imposed on a forming ormolding method. For example, processing methods used for ordinarythermoplastic resins, such as calendering, extrusion, blow molding andinjection molding, may be adopted.

[0061] 6. Resin Composition:

[0062] The graft copolymer according to the present invention can beblended with a thermoplastic resin to prepare a resin composition. Ablending ratio (based on solids content) between both may be suitablydetermined according to the purpose of use and desired properties. Ingeneral, they may be suitably selected within ranges of 0.1 to 99.9 wt.% for the graft copolymer and 99.9 to 0.1 wt. % for the thermoplasticresin. In many cases, good results can be yielded in proportions of 1 to99 wt. % for the graft copolymer and 99 to 1 wt. % for the thermoplasticresin. When the graft copolymer is blended as an impact modifier with athermoplastic resin such as a vinyl chloride resin, they may be oftenblended with each other in proportions of 1 to 50 wt. % for the graftcopolymer and 99 to 50 wt. % for the thermoplastic resin.

[0063] No particular limitation is imposed on the thermoplastic resin.As examples thereof, however, may be mentioned polystyrene, high impactpolystyrene (HI polystyrene resins), acrylic resins, methylmethacrylate-styrene resins (MS resins), vinyl chloride resins,chlorinated vinyl chloride resins, acrylonitrile-styrene resins (ASresins), acrylonitrile-butadiene-styrene resins (ABS resins),thermoplastic polyester resins and polycarbonate resins. Thesethermoplastic resins may be used either singly or in any combinationthereof.

[0064] Additives, for example, antioxidants, ultraviolet absorbents,anti-blocking agents, pigments, fillers, lubricants, antistatic agents,antibacterial agents, etc. may be suitably added upon the preparation ofthe resin composition. No particular limitation is imposed on a blendingmethod. Therefore, they may also be mixed with each other by means of aribbon blender, Henschel mixer or the like. This resin composition maybe subjected to molding or forming and processing as it is or afterpelletizing it. No particular limitation is imposed on a forming ormolding method. For example, processing methods used for ordinarythermoplastic resins, such as calendering, extrusion, blow molding andinjection molding, may be adopted.

[0065] When the resin composition comprising the graft copolymer and thethermoplastic resin is used as a transparent molded or formed product,it is desirable that the respective compositions be adjusted so as tolessen a difference in refractive index between the graft copolymer andthe thermoplastic resin in addition to the lessened difference inrefractive index between the polymer to be grafted and the graftcopolymer. When transparency is regarded as important, it is preferablethat the difference in refractive index between them be controlled to0.02 or smaller.

EXAMPLES

[0066] The present invention will hereinafter be described morespecifically by the following Examples and Comparative Examples.However, the present invention is not limited at all by these examples.Incidentally, all designations of “part” or “parts” and “%” as will beused in the following examples mean part or parts by weight and wt. %unless expressly noted. Physical properties in the examples weredetermined in accordance with the following respective methods.

[0067] (1) Volume Average Particle Diameter and Particle DiameterDistribution:

[0068] The volume average particle diameter (Dv; also referred to as“average particle diameter” merely) of each sample was determined bysubjecting an electron microscope photograph obtained by using atransmission type electron microscope to image analysis by an imageanalyzer (manufactured by Asahi Chemical Industry Co., Ltd.; IP-500PC).The particle diameter distribution (Dv/Dn) thereof was determined bycalculating out a ratio of the volume average particle diameter (Dv) toa number average particle diameter (Dn) obtained by subjecting thesample to image analysis in the same manner as described above.

[0069] (2) Refractive Index of Enlarged Latex-forming Component:

[0070] A cast film was formed with each enlarged latex sample, and theresultant cast film was immersed in methyl alcohol and then vacuum driedat room temperature for 24 hours, thereby preparing a sample film. Withrespect to the sample film, the refractive index was measured at 23° C.by means of an Abbe's refractometer.

[0071] (3) Refractive Indices of Graft Copolymer and ThermoplasticResin:

[0072] Each graft copolymer or thermoplastic resin sample was hotpressed at 200° C. to prepare a sample film. With respect to the samplefilm, the refractive index was measured at 23° C. by means of an Abbe'srefractometer.

[0073] (4) Impact Strength of Molded Product:

[0074] Specimen having a thickness of 3 mm or 6 mm were prepared bymeans of an injection molding machine IS-80 manufacture by ToshibaMachine Co., Ltd. With respect to these specimens, the impact strengthwas determined at 23° C. or −10° C. in accordance with JIS K 7110.

[0075] (5) Transparency of Molded Product:

[0076] Each graft copolymer or thermoplastic resin composition samplewas pelletized by means of an extruder and a pelletizer. The resultantpellet sample was hot pressed at 200° C. to prepare a sample platehaving a thickness of 3 mm. With respect to this sample plate, thetransmittance for parallel rays and haze were measured at 23° C. bymeans of a haze meter.

Example 1

[0077] 1. Preparation of latex:

[0078] After a pressure container equipped with a stirrer was chargedwith sodium chloride 0.075 parts ferrous sulfate 0.005 parts disodiumethylenediaminetetraacetate 0.008 parts sodium formaldehydesulfoxylate0.05 parts benzalkonium chloride (cationic 0.02 parts surfactant)potassium oleate (anionic surfactant) 0.37 parts distilled water 200parts and purged with nitrogen, diisopropylbenzene hydroperoxide 0.1parts butadiene 75 parts styrene 25 parts

[0079] were added. The contents were then held at 60° C. for 15 hours toconduct polymerization, thereby obtaining Latex (A-1) having aconversion of 98% and a volume average particle diameter of 98 nm.

[0080] 2. Enlargement by Aggregation:

[0081] While holding the Latex (A-1) obtained above at 70° C., sodiumformaldehydesulfoxylate 3.8 parts (5% aqueous solution) hydrogenperoxide (5% aqueous solution) 2.08 parts

[0082] were added, and the contents were stirred and mixed. The stirringwas then stopped to hold the mixture for 1 hour. Five parts of sodiumhydroxide (1% aqueous solution) were then added, and the contents werestirred and mixed to obtain Enlarged Latex (B-1). Enlarged Latex (B-1)had a volume average particle diameter of 460 nm and a Dv/Dn of 1.38 andwas mechanically stable. Incidentally, the sum total of deposits andattachments to the polymerizer was 0.05% based on the charged monomers.

Example 2

[0083] 1. Preparation of Latex:

[0084] Latex (A-2) having a conversion of 98% and a volume averageparticle diameter of 92 nm was obtained by conducting polymerization inthe same manner as in Example 1 except that 100 parts of butadiene wereused in place of 75 parts of butadiene and 25 parts of styrene in thepreparation of the latex in Example 1.

[0085]2. Enlargement by Aggregation:

[0086] Latex (A-2) obtained above was enlarged by aggregation in thesame manner as in Example 1 except that sodium formaldehydesulfoxylate4.2 parts (5% aqueous solution) hydrogen peroxide (5% aqueous solution)2.32 parts were added to Latex (A-2), thereby obtaining Enlarged Latex(B-2). Enlarged Latex (B-2) had a volume average particle diameter of500 nm and a Dv/Dn of 1.35 and was mechanically stable. Incidentally,the sum total of deposits and attachments to the polymerizer was 0.07%based on the charged monomers.

Example 3

[0087] 1. Preparation of Latex:

[0088] Latex (A-3) having a conversion of 98% and a volume averageparticle diameter of 98 nm was obtained by conducting polymerization inthe same manner as in Example 1 except that the amount of benzalkoniumchloride (cationic surfactant) was increased from 0.02 parts to 0.05parts in the preparation of the latex in Example 1, and 100 parts ofbutadiene were used in place of 75 parts of butadiene and 25% ofstyrene.

[0089] 2. Enlargement by Aggregation:

[0090] Latex (A-3) obtained above was enlarged by aggregation in thesame manner as in Example 1 except that sodium formaldehydesulfoxylate3.5 parts (5% aqueous solution) hydrogen peroxide (5% aqueous solution)1.9 parts were added to Latex (A-3), thereby obtaining Enlarged Latex(B-3). Enlarged Latex (B-3) had a volume average particle diameter of250 nm and a Dv/Dn of 1.40 and was mechanically stable. Incidentally,the sum total of deposits and attachments to the polymerizer was 0.04%based on the charged monomers.

Comparative Example 1

[0091] It was intended to obtain an enlarged latex in the same manner asin Example 1 except that no benzalkonium chloride (cationic surfactant)was added in the preparation of the latex in Example 1. Although anenlarged latex having an average particle diameter of 500 nm was formedafter holding the contents for 1 hour after the stirring was stopped inthe step of enlarging by aggregation, solids were deposited as lumps assoon as stirring was started after sodium hydroxide for neutralizationwas added, so that no stable enlarged latex was able to be obtained.

Comparative Example 2

[0092] Latex (A-1) having a volume average particle diameter of 98 nmobtained in Example 1 was used as seed particles to attempt thepreparation of a latex having a great particle diameter by a seedpolymerization process in place of the enlargement by aggregation.

[0093] After a polymerizer was charged with sodium chloride 0.075 partsferrous sulfate 0.005 parts disodium ethylenediaminetetraacetate 0.008parts sodium formaldehydesulfoxylate 0.05 parts potassium oleate 0.37parts Latex (A-1) (in terms of solids) 1 parts distilled water 200 partsand purged with nitrogen, the contents were held at 60° C., andbutadiene 74.25 parts styrene 24.75 parts diisopropylbenzenehydroperoxide 1 part sodium formaldehydesulfoxylate 0.5 parts

[0094] were then added over 60 hours. The contents were then held at 60°C. for 30 hours. As a result, the volume average particle diameter wasenlarged to 430 nm, but the conversion did not reach 95%.

Comparative Example 3

[0095] 1. Preparation of Latex:

[0096] After a pressure container equipped with a stirrer was chargedwith tetrasodium pyrophosphate 0.1 parts ferrous sulfate 0.005 partsdisodium ethylenediaminetetraacetate 0.008 parts sodiumformaldehydesulfoxylate 0.05 parts potassium oleate 0.37 parts distilledwater 200 parts and purged with nitrogen, diisopropylbenzenehydroperoxide 0.1 parts butadiene 75 parts styrene 25 parts

[0097] were added. The contents were then held at 60° C. for 15 hours toobtain Latex (a-3) having a conversion of 98% and a volume averageparticle diameter of 97 nm.

[0098] 2. Enlargement by Aggregation:

[0099] While holding the Latex (a-3) obtained above at 60° C., 0.2 partsof disodium dodecyl phenyl ether disulfonate were added, and the numberof revolutions upon stirring was then decreased. Although 1.2 parts ofphosphoric acid (5% aqueous solution) were added to conduct enlargementby aggregation, the latex was solidified.

Consideration

[0100] Example 1 shows an example where the present invention wasapplied to the butadiene-styrene copolymer latex, and Examples 2 and 3show examples where the present invention was applied to the butadienepolymer latices. In any case, a stable enlarged latex was obtained in ashort period of time.

[0101] On the other hand, Comparative Example 1 shows an example whereno cationic surfactant was used upon the preparation of thebutadiene-styrene copolymer latex. Even in the case of ComparativeExample 1, enlargement by aggregation is caused to progress. However,the restabilizing effect by the cationic surfactant upon lowering the pHof the system is not developed. Therefore, when sodium hydroxide wasadded to enhance the pH of the system, thereby attempting to stabilizethe system, solids are deposited due to shearing force by the stirring,resulting in a failure to obtain a stable enlarged latex.

[0102] Comparative Example 2 shows an example where it was intended toobtain a latex having the same particle diameter as in Example 1. Ittakes a very long time to conduct the polymerization. Therefore, theexample is poor in productivity and not an economical process.Comparative Example 3 shows an example where Example (A-2) described inJapanese Patent Application Laid-Open No. 71603/1998, in whichenlargement of particle diameter to 260 nm was achieved, was simulatedwith no cationic surfactant used, and the part of phosphoric acid addedwas increased so as to achieve a greater particle diameter. However, thelatex was solidified as a whole, resulting in a failure to obtain anenlarged latex.

Example 4

[0103] 1. Graft Polymerization:

[0104] After a pressure container equipped with a stirrer was chargedwith Enlarged Latex (B-1) 75 parts (in terms of solids) potassium oleate0.3 parts tetrasodium pyrophosphate 0.005 parts heated to 60° C. andpurged with nitrogen, styrene 12.5 parts methyl methacrylate 12.5 partsdiisopropylbenzene hydroperoxide 0.1 parts sodiumformaldehydesulfoxylate 0.05 parts

[0105] were added over 1 hour. The contents were then held for 5 hours.As a result, Graft Copolymer Latex (C-4) having a volume averageparticle diameter of 480 nm and a Dv/Dn of 1.35 was obtained.

[0106] After 0.5 parts of butylated hydroxytoluene (BHT) were added tothis Graft Copolymer Latex (C-4), coagulation was conducted with 0.5%hydrochloric acid, and the resultant coagulum was washed with water,dehydrated and dried to obtain a powdered Graft Copolymer (D-4). Therefractive index of the polymer (B-1) to be grafted in this GraftCopolymer (D-4) was 1.539, and the refractive index of Graft Copolymer(D-4) was 1.539.

Example 5

[0107] Graft Copolymer Latex (C-5) was obtained and Graft Copolymer(D-5) was recovered in the same manner as in Example 4 except thatsodium formaldehydesulfoxylate 3.3 parts (5% aqueous solution) hydrogenperoxide (5% aqueous solution) 1.8 parts

[0108] were used upon the enlargement of Latex (A-1) used in obtainingthe graft copolymer of Example 4 by aggregation. Graft Copolymer Latex(C-5) had a volume average particle diameter of 205 nm and a Dv/Dn of1.37. The refractive index of the polymer (B-5) to be grafted in thisGraft Copolymer (D-5) was 1.539, and the refractive index of GraftCopolymer (D-5) was 1.539.

Comparative Example 4

[0109] 1. Enlargement by Aggregation:

[0110] While holding the Latex (a-3) obtained in Comparative Example 3at 60° C., disodium dodecyl phenyl ether 0.05 parts disulfonate wasadded, and hydrochloric acid 56 parts (0.15% aqueous solution) was thenadded to conduct enlargement by aggregation, and sodium hydroxide (1%aqueous solution) 10 parts

[0111] was then added to obtain Enlarged Latex (b-4). Enlarged Latex(b-4) had a volume average particle diameter of 200 nm and a Dv/Dn of1.90 and was mechanically stable. Incidentally, the sum total ofdeposits and attachments to the polymerizer was 0.10% based on thecharged monomers.

[0112] 2. Graft Polymerization:

[0113] Enlarged Latex (b-4) was used to conduct graft polymerization inthe same manner as in Example 4, thereby obtaining Graft Copolymer Latex(c-4) having a volume average particle diameter of 205 nm and a Dv/Dn of1.85, and powdered Graft Copolymer (d-4) was obtained in the same manneras in Example 4. The refractive index of the polymer (b-4) to be graftedin Graft Copolymer (d-4) was 1.539, and the refractive index of GraftCopolymer (d-4) was 1.539.

Physical Properties of Resin Composition

[0114] Each of the graft copolymers obtained in Examples 4 and 5 andComparative Example 4 was used to prepare a resin composition with athermoplastic resin (MS resin) in accordance with the followingformulation, thereby determining its physical properties. The refractiveindex of the MS resin used was 1.540. Graft copolymer 30 parts MS resin(Denka TX-100, product of 70 parts Denki Kagaku Kogyo Kabushiki Kaisha)

[0115] The resin composition was pelletized by means of a twin-screwconical extruder having a diameter of 20 mm manufactured by Toyo SeikiSeisaku-Sho, Ltd., and the thus-obtained pellets were molded into aspecimen for impact test having a thickness of 6 mm by means of aninjection molding machine IS-80 manufactured by Toshiba Machine Co.,Ltd. The impact test was performed at 23° C. The results are shown inTable 1. TABLE 1 Physical properties of thermoplastic resin compositions(MS resin-based) Graft Impact strength Transmittance for Haze copolymer[kJ/m²] parallel rays [%] [%] Ex. 4 D-4 17.8 85 3.2 Ex. 5 D-5 5.8 90 1.7Comp. d-4 3.2 89 2.0 Ex. 4

[0116] As shown in Table 1, the resin composition comprising the graftcopolymer (Example 4) enlarged in particle diameter according to thepresent invention is achieved in a great improvement on impact strengthcompared with the resin composition comprising the graft copolymer(Comparative Example 4) prepared by using the ordinary technique forenlargement by aggregation though the transparency is slightlydeteriorated. The resin composition making use of the graft copolymer(Example 5) according to the present invention, which has the sameparticle diameter as that in Comparative Example 4 and a narrowerparticle diameter distribution, is improved in balance between impactstrength and transparency compared with the resin composition making useof the graft copolymer of Comparative Example 4.

Example 6

[0117] 1. Graft Polymerization:

[0118] After a pressure container equipped with a stirrer was chargedwith Enlarged Latex (B-3) 75 parts (in terms of solids) potassium oleate0.3 parts tetrasodium pyrophosphate 0.005 parts heated to 60° C. andpurged with nitrogen, methyl methacrylate 12.5 parts butyl acrylate 2.5parts t-butyl hydroperoxide 0.2 parts sodium formaldehydesulfoxylate 0.2parts were added over 1 hour. After the contents were then held for 3hours, styrene 10 parts t-butyl hydroperoxide 0.1 parts sodiumformaldehydesulfoxylate 0.1 parts

[0119] were added over 1 hour. The contents were then held for 5 hoursto obtain Graft Copolymer Latex (C-6) having a volume average particlediameter of 265 nm and a Dv/Dn of 1.37. Powdered Graft Copolymer (D-6)was obtained from this Graft Copolymer Latex (C-6) in the same manner asin Example 4.

Comparative Example 5

[0120] 1. Preparation of Latex:

[0121] After a pressure container equipped with a stirrer was chargedwith tetrasodium pyrophosphate 0.1 parts ferrous sulfate 0.005 partsdisodium ethylenediaminetetraacetate 0.008 parts sodiumformaldehydesulfoxylate 0.05 parts disodium dodecyl phenyl ether 0.02parts disulfonate potassium oleate 0.37 parts distilled water 200 partsand purged with nitrogen, diisopropylbenzene hydroperoxide 0.1 partsbutadiene 100 parts

[0122] were added. The contents were then held at 70° C. for 15 hours toobtain Latex (a-5) having a conversion of 98% and a volume averageparticle diameter of 95 nm.

[0123] 2. Enlargement by Aggregation:

[0124] While holding the Latex (a-5) obtained above at 60° C.,hydrochloric acid 60 parts (0.15% aqueous solution) was added to conductenlargement by aggregation, and sodium hydroxide (1% aqueous solution)10.7 parts

[0125] was then added to obtain Enlarged Latex (b-5). Enlarged Latex(b-5) had a volume average particle diameter of 220 nm and a Dv/Dn of1.87 and was mechanically stable. Incidentally, the sum total ofdeposits and attachments to the polymerizer was 0.12% based on thecharged monomer.

[0126] 3. Graft Polymerization:

[0127] Enlarged Latex (b-5) was used to conduct graft polymerization inthe same manner as in Example 6, thereby obtaining Graft Copolymer Latex(c-5) having a volume average particle diameter of 225 nm and a Dv/Dn of1.85, and powdered Graft Copolymer (d-5) was then obtained in the samemanner as in Example 4.

Physical Properties of Resin Composition

[0128] Each of the graft copolymers obtained in Example 6 andComparative Example 5 was used to prepare a resin composition with athermoplastic resin (vinyl chloride resin) in accordance with thefollowing formulation, thereby determining its physical properties. Morespecifically, the following blending components were provided andcharged into a Henschel mixer and heated to 115° C. with stirring toobtain a resin composition evenly mixed. Graft copolymer 9 parts Vinylchloride resin (“S9008”, 91 parts product of Kureha Kagaku Kogyo K.K.)Processing aid (“K130P”, product of 1.0 part Kureha Kagaku Kogyo K.K.)Octyltin mercaptide (“KS2000A”, 1.8 pats product of Kyodo Chemical Co.,Ltd.) Calcium stearate (“Ca-St”, product 0.5 parts of Nitto Kasei Co.,Ltd.) Ester-based lubricant (“SL-02”, 0.6 parts product of Riken VitaminCo., Ltd.) Titanium oxide (“DP-3T-55”, product 0.1 part of Resino ColorIndustry Co., Ltd.)

[0129] The resin composition thus obtained was pelletized by means of atwin-screw conical extruder having a diameter of 20 mm manufactured byToyo Seiki Seisaku-Sho, Ltd., and the thus-obtained pellets were moldedinto a specimen for impact test having a thickness of 3 mm by means ofan injection molding machine IS-80 manufactured by Toshiba Machine Co.,Ltd. The impact test was performed at 23° C. and −10° C. The results areshown in Table 2. TABLE 2 Physical properties of thermoplastic resincompositions (PVC-based) Graft Impact strength (23° C.) Impact strengthcopolymer [kJ/m²] (−10° C.) [kJ/m²] Ex. 6 D-6 116 41.0 Comp. d-5 11618.9 Ex. 5

[0130] As shown in Table 2, the resin composition comprising the graftcopolymer (Example 6) according to the present invention is achieved ina great improvement on impact strength at the low temperature comparedwith the resin composition comprising the graft copolymer (ComparativeExample 5) prepared by using the ordinary technique for enlargement byaggregation though the same impact resistance is exhibited at 23° C.

Industrial Applicability

[0131] According to the present invention, there is provided a processfor preparing an enlarged latex, which is economical and high inproductivity and permits enlarging a latex while retaining the stabilityof the latex. According to the preparation process of an enlarged latexaccording to the present invention, the stability of the latex is notimpaired even when a polymerizable monomer is graft polymerized in thepresence of the enlarged latex.

[0132] According to the present invention, there are also providedenlarged latices having such excellent various properties, a process forpreparing a graft copolymer by polymerizing a polymerizable monomer inthe presence of such an enlarged latex, resin compositions containingsaid graft copolymer and a thermoplastic resin, and graft copolymershaving a great particle diameter and an even particle diameterdistribution. The resin compositions according to the present inventionare economically improved in physical properties (particularly, impactresistance). Accordingly, the present invention can be applied tovarious fields in industries of which a latex having a great particlediameter and a graft copolymer having a great particle diameter arerequired.

1. A process for preparing an enlarged latex by enlarging a latex byaggregation, which comprises (1) causing (a) an anionic surfactant and(b) at least one surfactant selected from the group consisting of acationic surfactant and an amphoteric surfactant to exist in the latex,(2) adding, as an aggregating and enlarging agent, at least one selectedfrom the group consisting of: (i) an inorganic acid, (ii) an organicacid, (iii) a substance which forms an acid in water, (iv) a combinationof at least two substances which are reacted with each other to form anacid, and (v) a substance which forms an acid by exposure to active raysto the latex in the presence of these surfactants, and (3) causing theacid derived from the aggregating and enlarging agent to act on thelatex, thereby enlarging the particle diameter of the latex.
 2. Thepreparation process according to claim 1, wherein the latex is a(co)polymer latex of diene monomer(s), (co)polymer latex of vinylmonomer(s) or copolymer latex of a diene monomer with a vinyl monomer.3. The preparation process according to claim 1, wherein (a) the anionicsurfactant and (b) at least one surfactant selected from the groupconsisting of a cationic surfactant and an amphoteric surfactant areused as surfactants in the step (1) to emulsion polymerize themonomer(s), thereby causing these surfactants (a) and (b) to exist inthe latex.
 4. The preparation process according to claim 1, wherein theanionic surfactant is a carboxylate type anionic surfactant.
 5. Thepreparation process according to claim 1, wherein the cationicsurfactant is a quaternary ammonium salt having at least one alkylgroup, a primary to tertiary amine salt having at least one alkyl group,an alkylphosphonium salt or an alkylsulfonium salt.
 6. The preparationprocess according to claim 1, wherein the amphoteric surfactant is abetaine, a carboxylic acid type amphoteric surfactant containing abetaine, a sulfate type amphoteric surfactant or a sulfonic acid typeamphoteric surfactant.
 7. The preparation process according to claim 1,wherein in the step (1), (b) at least one surfactant selected from thegroup consisting of the cationic surfactant and the amphotericsurfactant is caused to exist in the latex in a proportion of 0.01 to100 mol per 100 mol of (a) the anionic surfactant.
 8. The preparationprocess according to claim 1, wherein in the step (1), the surfactants(a) and (b) are caused to exist in a proportion of 0.1 to 5 parts byweight in total per 100 parts by weight of the (co)polymer component inthe latex or the monomer(s) forming the (co)polymer component.
 9. Thepreparation process according to claim 1, wherein in the step (2), acombination of two substances which undergo a redox reaction to form anacid is used as (iv) the combination of at least two substances whichare reacted with each other to form an acid.
 10. The preparation processaccording to claim 9, wherein the combination of two substances whichundergo a redox reaction to form an acid is a combination of hydrogenperoxide with a formaldehydesulfoxylate.
 11. The preparation processaccording to claim 1, wherein in the step (3), the latex is enlarged byBrownian aggregation without conducting stirring of the latex.
 12. Thepreparation process according to claim 1, wherein an enlarged latexhaving a volume average particle diameter of at least 150 nm is providedby the enlargement by aggregation.
 13. The preparation process accordingto claim 1, wherein an enlarged latex having a particle diameterdistribution of 1.2 to 1.8, represented by a ratio (Dv/Dn) of the volumeaverage particle diameter (Dv) to the number average particle diameter(Dn) is provided.
 14. An enlarged latex obtained by the preparationprocess according to any one of claims 1 to
 13. 15. A process forpreparing a graft copolymer, which comprises polymerizing apolymerizable monomer in the presence of an enlarged latex, wherein theenlarged latex is obtained by a process comprising (1) causing (a) ananionic surfactant and (b) at least one surfactant selected from thegroup consisting of a cationic surfactant and an amphoteric surfactantto exist in a latex, (2) adding, as an aggregating and enlarging agent,at least one selected from the group consisting of: (i) an inorganicacid, (ii) an organic acid, (iii) a substance which forms an acid inwater, (iv) a combination of at least two substances which are reactedwith each other to form an acid, and (v) a substance which forms an acidby exposure to active rays to the latex in the presence of thesesurfactants, and (3) causing the acid derived from the aggregating andenlarging agent to act on the latex, thereby enlarging the particlediameter of the latex.
 16. The preparation process according to claim15, wherein the polymerizable monomer is a vinyl monomer.
 17. Thepreparation process according to claim 15, wherein 95 to 5 wt. % of thevinyl monomer is polymerized with 5 to 95 wt. %, in terms of solids, ofthe enlarged latex.
 18. The preparation process according to claim 15,wherein a graft copolymer having a particle diameter distribution of 1.2to 1.8, represented by a ratio (Dv/Dn) of the volume average particlediameter (Dv) to the number average particle diameter (Dn), is obtained.19. The preparation process according to claim 15, wherein a differencein refractive index between particles of the enlarged latex and thegraft copolymer formed is at most 0.02.
 20. The preparation processaccording to claim 15, wherein a graft copolymer having a volume averageparticle diameter of at least 150 nm is obtained.
 21. A graft copolymerobtained by the preparation process according to any one of claims 15 to20.
 22. A resin composition comprising the graft copolymer according toclaim 21 and a thermoplastic resin.
 23. The resin composition accordingto claim 22, which comprises 0.1 to 99.9 wt. % of the graft copolymerand 99.9 to 0.1 wt. % of the thermoplastic resin.
 24. The resincomposition according to claim 22, wherein the thermoplastic resin ispolystyrene, high impact polystyrene, acrylic resin, methylmethacrylate-styrene resin, vinyl chloride resin, chlorinated vinylchloride resin, acrylonitrile-styrene resin,acrylonitrile-butadiene-styrene resin, thermoplastic polyester resin,polycarbonate resin or a mixture thereof.
 25. A graft copolymercontaining an anionic surfactant and at least one surfactant selectedfrom the group consisting of a cationic surfactant and an amphotericsurfactant and having a ratio (Dv/Dn) of the volume average particlediameter (Dv) to the number average particle diameter (Dn) of 1.2 to1.8.
 26. The graft copolymer according to claim 25, wherein the volumeaverage particle diameter (Dv) is at least 150 nm.
 27. A resincomposition comprising the graft copolymer according to claim 25 and athermoplastic resin.